3

Extinction!

Mass extinctions. Dinosaurs
and the first mammals. Saving an unspoiled forest near Bangkok. Biological
invaders in the Hawaiian Islands. Using a beneficial insect to control
weeds in North Dakota.

A. The Permian Extinction

As leaves fall from a
tree--presumably a symbol for Darwin's tree of life--University
of Washington paleogeologist Peter D. Ward tells us: "Extinction
is the termination of a species." At least 95 per cent of all
species that have ever lived are now extinct. Extinction is normal,
he says, and is happening all the time, at the rate of a few species
per year.

We watch various animals
foraging for food, and a lioness bringing down her prey. "The
extinction of old species that can no longer adapt or compete creates
opportunities for new species that can--in an endless cycle,"
the narrator says. "So evolution and extinction are in balance.
But what happens when a planet-wide catastrophe strikes and a great
dying begins?"

The scene changes dramatically--to
lightning, volcanoes, and fire. Five times in the last half-billion
years, we are told, mass extinctions wiped out most species alive
at the time. As the smoke clears, we see Peter Ward driving through
South Africa to investigate the greatest of these mass extinctions--the
one that occurred at the end of the geological period known as the
Permian. He stops at an old abandoned farmhouse, and sees from the
tombstones in a nearby graveyard that the family that used to live
there died within a five-year period about a century ago. "So
a hundred years [ago], these people were just wiped off the face
of the Earth, and we have no idea what killed them," says Ward.
"And if that's the case, how am I going to figure out what
killed animals that lived in those hills [gesturing], the fossils
of which we have from 250 million years ago?"

Ward explains: "You
could almost analogize that to a house of cards. Each species props
up another, in a sense." We watch as a huge house of playing-cards
teeters in front of us. Ward continues: "Because the creature
that you eat is that card that is sitting under you that gives you
your energy. Now let's pretend that we start kicking out card after
card after card--and that's what a mass extinction does, isn't it?
It starts knocking out a species here, it knocks out a species there,
but pretty soon lots of species are gone. And it's not just the
disappearance of species now--the whole house of cards falls down."

Not everything died in
the Permian extinction, however. Ward holds up the skull of a mammal-like
reptile. He says that the few lineages that survived the extinction
"start evolving, because the world is empty, and empty worlds
really begat [a] tremendous amount of evolutionary diversifications."

But how do empty worlds
beget new species, exactly? Mass extinction may be an important
feature of the history of life; but the question is, how did living
things diversify afterwards? That is
the question Darwin's theory is supposed to answer, but the fact
of extinction doesn't help us. Species go extinct, and new ones
take their places. This may come as a surprise to people who believe
that species never go extinct (if, in fact, there are such people);
but how does it provide evidence for Darwinian evolution?

The scene shifts to the
American Museum of Natural History in New York City, where mammal
curator Michael J. Novacek tells us about his childhood fascination
with stories of dinosaur fossils found by Roy Chapman Andrews in
the Gobi Desert in China. Years later, Novacek went to the Gobi
Desert himself--but to look for fossils of early mammals instead.

Novacek explains that
early mammals were quite small, dwarfed by the dinosaurs who were
their contemporaries. After millions of years another mass extinction
occurred, at the end of the Cretaceous period, perhaps caused by
a large asteroid that landed in what is now the Gulf of Mexico.
This global catastrophe wiped out the dinosaurs--in a chain reaction
dramatized once again by a falling house of cards.

The narrator tells us
that the mammals survived because they were small and "could
take refuge underground." When they re-emerged after the "K-T
event" (K stands for Cretaceous and T for Tertiary, the geological
period following the catastrophe), the dinosaurs were gone, and
the world belonged to them. "Mass extinction made them evolution's
big winners--by default."

As we are treated to
more beautiful wildlife photography, the narrator tells us that
mammals--freed from having to compete with the dinosaurs--"spread
out to all parts of the world. They filled every empty niche. They
competed, adapted, and diversified, until most of the world's largest
animals were mammals. Then, around 5 million years ago, the first
human precursors emerged in Africa--mammals that would play an unprecedented
role in evolution's future." Bleached bones stick out of the
dry soil, and we view a trail of footprints as the narrator explains:
"They began to walk upright. They left their footprints in
volcanic ash that hardened. They evolved into the genus Homo--humankind."

This makes an interesting
story. But the K-T event, like the Permian extinction, does not
help us to understand evolution. Instead of saying that mass extinction
made the survivors "evolution's big winners," the narrator
might just as well have said "history's big winners,"
or "life's big winners." Using the word evolution doesn't
add a thing here--except perhaps to give us the impression that
an explanation has been provided, when in fact none has.

The fossil skulls we
saw certainly provide evidence that there were animals living in
the past that are no longer with us, and they suggest that some
of those animals had features intermediate between ancient reptiles
and modern mammals. As we saw in Episode Two, however, fossils by
themselves cannot provide evidence for ancestry and descent, much
less evidence that the process occurred through natural selection.
Life has a history. But was that history due to Darwinian evolution?

The scene shifts to Bangkok,
Thailand. "Today," the narrator continues, "the world
is bursting at the seams with people." Bangkok, we are told,
has doubled in size in the last two decades, and now has more than
10 million inhabitants. In the past ten thousand years, we have
out-competed--and thus driven extinct--many other species. The narrator
concludes: "We may be the `asteroid' that brings on the sixth
great mass extinction."

C. Studying a Remote
Forest

We fly over a mist-shrouded
valley as the narrator describes a national park to the west of
Bangkok, where the human population is nil. Wildlife Conservation
Society scientist Alan Rabinowitz came here to study the ecosystem.

Rabinowitz says: "We're
in grave danger of the `empty forest syndrome'--having a beautiful,
seemingly intact forest on the surface, but inside that forest the
natural components which maintain the flow of energy through the
system--which has developed through millions of years of evolution--it's
disrupted. Now people say, So what does it matter if one component's
gone? What if you don't have the Sumatran rhino? What if the civet
species are all gone--or other things? But each thing has evolved
to play an incredibly important role within this complex puzzle."

The narrator explains
that Rabinowitz is here to find out if the forest still has a balanced
ecosystem in which evolution can continue without being affected
by the increasing rates of extinction elsewhere. He is especially
interested in large carnivores. Since they depend on species below
them in the energy chain, they're the first to go when the ecological
house of cards begins to collapse.

"There's no doubt
that the major cause of extinction on a global level is human-related,"
he says. "Everything from clear-cutting forests, to removing
intact habitats, to just desecrating them, changing them."
The narrator adds: "Habitat destruction is the number one cause
of extinction."

D. Biological Invaders

The scene shifts to the
Hawaiian Islands, as the narrator explains how they were formed
from undersea volcanoes and then colonized by living things from
distant lands. "Thousands of species made it by sea or by air.
They evolved until they were found nowhere else on earth."

Fordham University paleoecologist
David A. Burney and his son explore the Hawaiian Islands "to
better understand what happened after the Polynesians arrived"
centuries ago. We watch as Burney drains a sinkhole, "revealing
ten thousand years of sediment and a story of evolution that's just
as long."

Burney finds evidence
that the Polynesians brought stowaway rats and a few other non-native
species with them. But the Europeans brought many more. "We're
now to the point," Burney says, "where there are about
a thousand native species of plants in the Hawaiian Islands and
over a thousand naturalized invasive species--things that have been
introduced by people. Evolution has now entered a new mode. Something
new altogether is happening, and it has to do with what humans do
to the evolutionary process."

The scene shifts to various
modes of air and sea transport, as the narrator explains how hitchhiking
species colonize virgin territories and become pests. A Hawaiian
agricultural inspector talks about the difficulty of keeping biological
invaders out of the islands, and Burney predicts that biological
invasions will be visible in the fossil record a million years from
now.

"Scientists have
a term for biological invaders," the narrator tells us. "They
call them `weed species.' Like weeds, they survive and adapt almost
anywhere, and push out the native species--sometimes to the point
of extinction. They are the ultimate survivors."

After Novacek returns
to speculate briefly on why biological invaders tend to be so successful,
the narrator continues: "Of all the weed species on earth,
we [human beings] are the most mobile, the most adaptive, and the
most flexible--by far. The good news is, we'll probably be around
for a long time. The bad news is, the world around us may be very
different. Every species we drive towards extinction, no matter
how inadvertently, is one less species that might help prop up the
others."

Re-enter Peter Ward,
who ties this thread back into the main theme of the episode: "So
the question is, in our own modern world, with our own house of
cards, How close are we to that whole edifice coming down? Have
we reached that threshold?"

Curiously, there are
several unanswered questions in what we have just been told. First,
what, exactly, favors evolution? Does evolution proceed mainly when
there is intense competition for survival, as Darwin proposed? Or
does it proceed mainly when competition is eliminated through mass
extinction, or through migration to an uninhabited island? Maybe
it's both. Or maybe it's neither.

Second, is extinction
good or bad? From an evolutionary perspective, it seems, extinction
is a good thing, since it provides opportunities for surviving organisms
to diversify. From a human perspective, however, our own extinction
would be a bad thing, so we should interfere with evolution to preserve
ourselves. Why, then, do we need an evolutionary perspective?

Third, What does evolution
have to do with how some species replace other species over a span
of ten thousand years? None of the species are changing. We saw
more evolution in bacteria that develop resistance to antibiotics--and
even that didn't really help Darwin's theory about the
origin of species.

E. Leafy Spurge

The scene shifts to the
rolling grasslands of North Dakota. "It's where one of the
battles against human-caused extinction is being fought," the
narrator says. "The enemy here is a weed called `leafy spurge'--so
adaptive and tenacious, it threatens to kill off all the native
grasses. It's already spread across a million acres. Accidentally
brought by pioneers in bags of seeds a century ago, the settlers'
descendants are now faced with the consequences."

A rancher explains that
leafy spurge limits the number of cattle he can put in a pasture,
because the cattle won't eat the grass if it is infested with the
weed. "I look at it as cancer to the land," the rancher
says, "and it makes the land just totally useless." There
is a chemical available that kills leafy spurge, but it is prohibitively
expensive.

The narrator continues:
"If the chemical won't stop it, what's left? How can the farmers
fight back against a super-adaptive invader that threatens to drive
native species to the brink of extinction, and take over their ecological
niche? The solution may be another invader--discovered when scientists
learned what kept leafy spurge in check in its native Russia. It's
the flea beetle--a case of fighting evolutionary fire with fire."
Flea beetles eat leafy spurge, and thereby help to keep it under
control.

We watch as North Dakota
ranchers spread flea beetles throughout their pasturelands in an
effort to control leafy spurge. Then the narrator says: "So
now we're in a race most of us don't even know we're running--to
learn as much as we can about the meaning and message of extinction
before it's too late."

But extinction has nothing
to do with the leafy spurge story. Although the weed is out-competing
native grasses in some areas, it is an exaggeration to say that
it "threatens to drive native species to the brink of extinction."
Furthermore, it does not render land "totally useless,"
except to cattle ranchers. Although cattle are repelled by leafy
spurge, sheep and goats are not; the latter even seek it out.

F. What's Evolution
Got To Do With It?

The scene then shifts
back to Alan Rabinowitz in Thailand. Happily, the other teams of
scientists working with him had more success with their cameras
than he had. Their films show that the forest is still populated
with large carnivores, and thus still has a healthy ecosystem.

Rabinowitz reflects on
the implications of this: "There are still places left where
the natural evolutionary processes are going on. Most of my career
involves documenting extinction, or species on the verge of extinction.
But every now and then, you get a place like this. And you say,
It's not lost yet. It's not gone yet. Knowledge is definitely our
greatest tool against extinction--there is no, no doubt about it.
Without knowledge, we continue in the dark. Many species are on
a very quick downward slide, possibly to extinction, faster than
they would be normally, because of human-related activities. But
we're not at an end-point here, by any means. We're still in the
middle of a completely complex, changing scenario. Evolution is
going on around us."

The "evolution"
that Rabinowitz sees going on around us, however, is not "evolution"
in Darwin's sense. The "evolution" to which Rabinowitz
refers involves the displacement of some species by others, but
the "evolution" that matters in Darwin's theory is the
origin of new species. And there is no evidence here for the latter.

The episode closes with
a reading from Darwin's The Origin of Species: "We need not
marvel at extinction. If we must marvel, let it be at our own presumption
in imagining for a moment that we understand the many complex contingencies
on which the existence of each species depends. The appearance of
new species and old species are bound together."

What does this last statement
mean? Species go extinct, and new ones appear to take their places.
But we still have seen no evidence of one species changing into
another--much less through natural selection, as Darwin claimed.
Extinction, as Peter Ward explained, is the termination of a species,
not its transformation.

Extinction happens. But
what's evolution got to do with it?

Notes

.
For more information on mass extinctions, see Peter D. Ward, Rivers
in Time: The Search for Clues to Earth's Mass Extinctions (New
York: Columbia University Press, 2001)

Based on new
fossil discoveries, some scientists are now questioning whether
the "Big Five" mass extinctions were really as big as
previously believed. See Richard A. Kerr, "Mass Extinctions
Facing Downsizing, Extinction," Science 293 (2001), 1037.

.
Although not much is said about them here, mammal-like reptiles
are often cited as good evidence for Darwinian evolution. Not
surprisingly, however, the story is more complicated than promoters
of Darwinian evolution make it out to be. For one review, see
Ashby L. Camp, "Reappraising the Crown Jewel," at:

http://www.trueorigins.org/therapsd.htm

.
Alan Rabinowitz's work in Thailand and neighboring Myanmar was
done under the auspices of the World Conservation Society, which
is affiliated with the Bronx Zoo in New York. For more information,
see:

http://wcs.org/home/wild/Asia/tiger

http://wcs.org/home/wild/Asia/2688

.
Leafy spurge produces an irritating sap that is harmful and distasteful
to cattle, so it renders grazing land unsuitable for cattle. As
this episode mentions, flea beetles are one way to control leafy
spurge. Other ways to control it without resorting to chemical
pesticides include grazing with sheep or goats (goats actually
seek it out), or planting wheat grass or wild rye. For general
information about leafy spurge, go to:

http://users.aol.com/prideedu/leafy.htm.

For more information
about the biological control of leafy spurge, go to:

http://www.ext.nodak.edu/extpubs/plantsci/weeds/w866w.htm

http://www.ext.nodak.edu/extpubs/plantsci/weeds/w1183w.htm

Although the
use of flea beetles (as described in this episode) did not start
until the 1980s, there is nothing new about biological control.
In China and Yemen, farmers have been using ants to control crop
pests for centuries. In India, intercropping (planting mixed crops
to combat pests) has been used for centuries. Such ancient practices
obviously owe nothing to Darwin or his theory. Here are some quotes
from web sites of interest:

Biological pest
control was used by the ancient Chinese, who used predacious ants
to control plant-eating insects. In 1776, predators were recommended
for the control of bedbugs.

http://www.comptons.com/encyclopedia/ARTICLES/0125/01429248_A.html

The Chinese
were far ahead of the Western world in natural pest control. In
the countryside frogs were always a forbidden food because they
ate insects. Praying mantises were released in gardens among the
chrysanthemums to drive away leaf-eating insects. The most remarkable
and economically important of the ancient Chinese biological weapons
was the yellow citrus killer-ant. Its use is described in Hsi Han's
Records of the Plants and Trees of the Southern Regions, written
in A.D. 340: "The Mandarin Orange is a kind of orange with
an exceptionally sweet and delicious taste. . . . The people of
Chiao-Chih sell in their markets [carnivorous] ants in bags of rush
matting. The nests are like silk. The bags are all attached to twigs
and leaves, which, with the ants inside the nests, are for sale.
These ants do not eat the oranges, but attack and kill the insects
which do. In the south, if the mandarin orange trees do not have
this kind of ant, the fruits will be damaged by the many harmful
insects, and not a single fruit will be perfect.

http://www.inventions.org/culture/ancient/pest.html

Yemenis were
among the earlier nations that used biocontrol agents for the control
of agricultural pests. . . . In traditional agriculture farmers
in Tihama, Taiz and Hadramout used to collect predatory ants (qu'as)
from mountains to control date palm pests which attack fruits. This
has been described in a 13th century agricultural text by al-Malik
al-Ashraf `Umar of Rasulid, Yemen. . . . When we asked old farmers
about this practice they confirm that. They added that they have
to put some sticks to make ants to travel from one tree to another.

http://www.aiys.org/webdate/pelbaa.html

Intercropping
in India: Farmers in the developing world have been growing two
or more crops together on the same piece of land for many centuries.
In India, as many as 84 different crops are used in mixed cropping,
but seldom do we find more than four at a time, and a relatively
simple mixture of only two or three crops is most common. . . .
Although research on intercropping may have started to provide an
understanding of why the farmer used such mixtures, and to help
improve his productivity in ways relevant to his practice, it has
now been shown that intercropping may have several advantages over
sole cropping. It appears to make better use of the natural resources
of sunlight, land, and water. It may have some beneficial effects
on pest and disease problems, although the overall results are somewhat
inconclusive.

http://ourworld.compuserve.com/homepages/rbmatthews/rbm_ic1.htm

.
Peter Grant's comment about ecology is from "What Does It
Mean to Be A Naturalist at the End of the Twentieth Century?"
The American Naturalist 155 (2000), 1-12, 9.